The Impact of North Atlantic Oscillation on the Atmospheric Pollutant Variability in the Porto Region, Portugal .

The North Atlantic Oscillation (NAO) is an important large-scale atmospheric circulation that influences the European countries climate. This study evaluated NAO impact in the air quality in Porto Metropolitan Area (PMA), Portugal, for the period 2002-2006. NAO, air pollutants and meteorological data were statistically analyzed. All data were obtained from PMA Weather Station,PMA Air Quality Stations and NOAA analysis. Two statistical methods were applied in different time scale: principal component and correlation coefficient. Annual time scale, using multivariate analysis (PCA, principal component analysis), were applied in order to identified positive and significant association between air pollutants, such as PM1O, PM2.5, CO, NO and N02, with NAO. On the other hand, the correlation coefficient using seasonal time scale analysis were also applied to the same data. The results of PCA analysis present a general negative significant association between the total precipitation and NAO, in Factors 1 and 2 (explaining around 70% of the variance), presented in the years of 2002, 2004 and 2005. During the same years, some air pollutants (such as PM1O, PM2.5, S02, NOx and CO) present also a positive association with NAO. The 03 shows as well a positive association with NAO during 2002 and 2004, at 2nd Factor, explaining 30% of the variance. From the seasonal analysis using correlation coefficient, it was found significant correlation between PM1O (0.72., p<0.05, in 2002), PM2.5 (0 74, p<0.05, in 2004), and S02 (0.78, p<0.01, in 2002) with NAO during the March-December (no winter period) period. Significant associations between air pollutants and NAO were also verified in the winter period (December to April) mainly with ozone (2005, r= -0.55, p<0.01). Once that human health and hospital morbidities may be affected by air pollution, the results suggest that NAO forecast can be an important tool to prevent them, in the lberian Peninsula and specially Portugal.